Manufacture of electron discharge tubes



Dec. 5,1950 1. H. JONKER 2,532,846

. I MANUFACTURE OF ELECTRON DISCHARGE TUBES Filed July 22, 1949 Patented Dec. 5, 1950 v UNITED STATE MANUFACTURE OF ELECTRON DISCHARGE. 1i. a

TUBES Johannes Lodewijk Hen Netherlands, assignor Bank and Trust Company, Hartford, Conn., as

trustee drik Jonker, Eindhoven,

to Hartford National Application July 22, 1949, Serial No. 106,115

the Netherlands July 22, 1948 '2 Claims. (01. 3161'7) The invention relates to the method of manufacture of electron discharge tubes having small inter-electrode spacings. The invention furthermore relates to a tube so manufactured.

It is known to manufacture electron discharge tubes having small inter-electrode spacin s between electrodes by arranging the electrodes in contact with each other whilst a glass mass provided between supports for the electrodes is soft, it being immaterial whether or not the electrodes are heated to a high temperature. On cooling, the glass hardens and owing to the difference between the coefficients of thermal expansion of metal and glass, the electrodes are retracted from each other by a definite distance. This method has a limitation in that the cooling glass is apt to be subjected to stresses liable to upset the parallel relationship between the electrode surfaces.

It is an object of the present invention to provide a method of manufacturing an electron discharge tube having a small inter-electrode spacing. in which the aforesaid limitation is obviated and which method has the advantage that the final inter-electrode spacing does not var with the hardening temperature of the glass but instead is adjustable by means of a temperature employed during manufacture Of the tube.

In the method according to the invention of manufacturing electron tubes having small interelectrodes spacings at least one of the electrodes between which the small spacing must be adjusted is arranged in a metal cylinder so as to be slidable in the axial direction of the electrode system and the electrodes while in contact with one another are heated to a temperature exceeding the operation temperature by a predetermined number of degrees, the slidable sleeve then being secured in place by solder. The final spacing at the normal operation temperature varies with the coeflicients of thermal expansion of the materials of which the electrodes are made and of the insulators by which the electrodes are secured in place relatively to one another.

In order that the invention may be more clearly I understood and readily carried into effect, it will now be described more fully with reference to the accompanying diagrammatic drawing.

Referring to the drawing, l designates the glass wall of the discharge tube, in which a copper disc 2 terminating in a cylinder '3 is s aled. A cop er cylinder 4 is adapted to slide within the cylinder 3. Arranged on top of the copper sleeve 4 with the use of a molybdenum foil 5 is a cathode 6, which is adapted to be heated by means of a filament coil 8. The current for the filament coil 8 is fed by two wires 9, which are insulated from the sleeve 4 and from one anothe by two ceramic cylinders 10. The cathode has arranged opposite to it an anode H, the front surface l2 of which is suitably surface-ground so as to be parallel to the surface of cathode 6. Use is preferably made of a cathode without a sprayed emissive layer. During manufacture the tube is arranged in a position inverted in relation to that shown in the drawing so that the anode is downwards'and since the sleeve 4 is free to move within the cylinder 3, the cathode 6 rests on the anode surface l2. With the use of the filament coil 8 the cathode is heated to a definite temperature exceeding the normal operation temperature. After the temperature distribution of the tube has become constant a tin ring l3 arranged between the cylinder 3 and the sleeve 4 is melted, for example, with the use of high-frequency currents. Owing to the capillary effect, the tin flows between 3 and 4 and thus joins these parts together. In order to prevent the tin from melting at the subsequent operating temperature of the cathode, the soldering area is heated till the whole of the tin is alloyed. When the cathode temperature is then reduced to the normal operation temperature, the foil 5 will be subject to greater shrinkage than the surrounding glass wall, so that a small spacing will be produced between the surfaces 6 and I2. The size of this spacing is determined by the length and the thermal expansion coefficient of the foil 5. by the height of the disc 2 and its thermal expansion coefficient, the length of the wall between 2 and II and the length of the anode II and their thermal expansion coefiicients and their temperatures. It has been found that in this manner tubes having cathode-anode spacings of the order 0f 5; can be produced in a reproduceable manner.

What I claim is;

l. A method of manufacturing electron discharge tubes having small inter-electrode spacings, characterized in that at least one of the electrodes between which the small spacing must be adjusted is arranged in a metal cylinder so as to be slidable in the axial direction of the electrode system and the electrodes are then heated to a predetermined temperature exceeding the operation temperature while in contact with one another, the slidable sleeve being then secured in place by soldering.

2. A method of manufacturing electron discharge tubes having small anode-cathode struc- 3 ture spacings and in which tubes the cathode is REFERENCES CITED arranged in metal cylinder and is adjustable The following references are of record in the along the anode-cathode axis, comprising the file of this atent: steps of positioning the anode and cathode in p contact vrelation, heating the contacting anode 5 UNITED STATES PATENTS and cathode toa predetermined temperature ex- Number Name Date ceeding the tube operation temperature, and se- 2,428,610 Beggs Oct. 7, 1947 curing the metal cylinder and cathode structure 2,450,197 Ishler Sept. 28, 1948 in position by solder.

JOHANNES LODEWIJK HENDRIX JQNKER. ll 

